Pascoe, P. P. | Search bioRxiv

bioRxiv2021

Using camera traps to determine occupancy and breeding in burrowing seabirds

Burrowing seabirds are important in commercial, ecological and conservation terms. Many populations are in flux owing to both negative and positive anthropogenic impacts, but their ecology makes measuring changes difficult. Reliably recording key metrics, the proportion of burrows with breeding pairs, and the success of breeding attempts, requires burrow-level information on occupancy. We investigated the use of camera traps positioned at burrow entrances for determining the number of breeding pairs in a sample to inform population estimates, and for recording breeding success. Linear Discriminant Analyses of time series activity patterns from camera traps successfully partitioned breeding and non-breeding burrows at different stages of the breeding season and had reasonable predictive ability to determine breeding status on a small test dataset. Compared with traditional techniques for determining burrow occupancy (e.g. manual burrow inspection and playback of conspecific calls at burrow entrances), camera traps can reduce uncertainty in estimated breeding success and potentially breeding status of burrows. Significant up-front investment is required in terms of equipment and human resources but for long-term studies camera traps can deliver advantages, particularly when unanticipated novel observations and the potential for calibrating traditional methods with cameras are factored in.

ecology↗

bioRxiv2021

Detecting seabird responses to invasive species eradication

Maximising survey efficiency can help reduce the trade-off between spending limited conservation resources on evaluating performance of past interventions and directing those resources towards future interventions. Seabird responses to island eradications are often poorly evaluated owing to financial, logistical and methodological challenges associated with remote field work and species ecology. We surveyed an assemblage of threatened seabirds following the worlds largest island eradication of multiple invasive species, testing multiple survey designs and outputs. We compared the outcomes of two important choices made during survey design: 1) whether to use unbiased or targeted surveys; and 2) implementing design-based or model-based analyses. An unbiased whole-island stratified randomised survey design performed well in terms of confidence in the final population estimates for widespread species, but poorly for localised recolonising species. For widespread species, model-based analyses resulted in slightly lower population estimates with narrower confidence intervals than traditional design-based approaches but failed to capture the realised niches of recolonising species, resulting in population estimates three orders of magnitude higher than current best estimates. We conclude that a multi-method approach to survey design best captures the size and distribution of recovering populations when the study system is ecologically diverse--importantly our results suggest there is no single strategy for efficient surveys of diverse seabird communities following large island invasive species eradications.

ecology↗